Telescoping seating structures are most often used in school gymnasiums to provide temporary bleacher-type seating for sports events. In the extended position for seating use, the structure extends forwardly from a rear wall on the perimeter of a floor surface, with rows of seats arranged stepwise downward from the rear wall. When temporary seating is not required and the full floor surface is needed for athletic or other use, the structure is moved rearwardly to a retracted position for storage against the rear wall, with the rows superposed vertically above each other and the risers of the rows forming a vertical front plane.
In conventional telescoping seating structures each row is supported by a forwardly extending cantilevered arm fixed to a vertical post of predetermined height. When the seating structure is in the extended position, with the rows in stepped relation, the free end of each cantilevered arm is supported by the upper end of the vertical post of the next forward row, providing a sturdy support for each row. A problem is presented in supporting the seats when the structure is in the retracted position, with the rows supported only by the cantilevered arms.
Bystanders and other persons sometimes climb on the front risers in the front plane of the retracted structure, placing large loads on the forward free ends of the cantilevered arms. Under such loads, which can exceed 200 pounds, the free end of the cantilevered arm of each loaded row deflects downwards, engaging the seating surface of the next lower row, and that row with the next lower, and so on, until either a sufficient number of rows are engaged to carry the entire load, or until the seating surface of the bottommost row of seats is engaged.
The gap between the front riser of each row and the seating surface of the next lower row may be only a fraction of an inch. The bottommost row does not deflect at all, being fixedly supported by the wheels of the carriage assembly of that row. Under the load from a person climbing the front face of the retracted telescoping seating structure, the second row, immediately above the bottommost row, will deflect a distance no more than the width of the clearance gap between those rows. The third row, immediately above the second row, will deflect up to twice that distance; the fourth row will deflect up to three times that distance; and so on, up to the row supporting the climber. The cumulative deflection imposed on the upper loaded rows can be sufficient to cause permanent deformation of their cantilevered arms. The permanent deformation which occurs may prevent movement of the seating structure from its extended position to its retracted position.
A further problem is presented when the seating structure is used in a location with an uneven floor surface. The unevenness may produce a lack of vertical alignment of the rows as a result of the different heights of the rear supporting vertical posts, which are each carried by a wheeled carriage engaging the floor. If the floor surface is excessively uneven, the clearance gaps between the risers may close completely or overlap, preventing movement of the seating structure from its extended position to its retracted position and requiring time-consuming precision adjustment of the seating structure or expensive resurfacing of the floor surface.